A type of control apparatus for an internal combustion engine has been proposed that performs a delay control for extending the period from when an engine stop request (for example, the driver's turning off the ignition switch) is made to when the engine is actually stopped.
For example, Japanese Laid-Open Patent Publication No. 2002-161766 discloses a configuration for executing delay control in an internal combustion engine having a variable valve actuation mechanism for changing valve parameters of the engine valves such as intake valves and exhaust valves. The internal combustion engine disclosed in the publication has a hydraulic pump driven by the power of the engine. Hydraulic pressure generated by the hydraulic pump is used to actuate the variable valve actuation mechanism. The variable valve actuation mechanism is activated after the delay control is started to change the valve parameter to a state suitable for the next starting of the engine. This improves the startability of the engine in the next starting.
In this manner, the power of the engine is not only used as a power source of the vehicle, but also as a power source for actuating auxiliary devices such as the hydraulic pump, a compressor of a vehicle air-conditioner, and an alternator.
When the driving load of the auxiliary devices is increased with respect to the engine power, a corresponding amount of the engine power is consumed for driving the auxiliary devices. This reduces the engine speed. Thus, a load compensation control is normally executed in which the engine power is adjusted in accordance with the driving load of the auxiliary devices. One example of such load compensation control is an idle speed control executed during idling. In the idle speed control, the engine power is adjusted such that the engine speed during idling seeks a predetermined target idle speed. For example, when the load of the auxiliary devices increases and the engine speed is less than a target engine speed, the intake air amount is increased. The fuel injection amount is increased accordingly. This increases the engine power, so that the engine speed is increased to the target idle speed. Since the driving load of the compressor is greater than that of other auxiliary devices, the target idle speed is set higher when the compressor is operating than when it is not operating.
In an internal combustion engine that executes the load compensation control, the execution of the delay control is expected to cause the following disadvantages.
When an engine stop request is made while auxiliary devices are operating, the auxiliary devices are stopped. The intake air amount that has been increased in accordance with the driving load of the auxiliary devices is reduced according to the reduction in the driving load caused by stopping of the auxiliary devices. Since the rate at which the intake air amount is reduced is less than the rate of reduction in the driving load caused by stopping of the auxiliary devices, a response delay occurs in reduction in the engine power relative to the reduction in the driving load according to the stopping of the auxiliary devices.
In the case of an internal combustion engine that does not execute the delay control, such a response delay accompanying reduction in the engine power is unlikely to occur since the engine is stopped immediately after an engine stop request is made.
On the other hand, an internal combustion engine that executes the delay control continues operating for a certain period of time after an engine stop request is made. Therefore, the above described response delay occurs when the engine power is reduced after the engine stop request is made. Such a response delay during the delay control results in a period in which the engine power is not sufficiently reduced even if the driving load of the auxiliary devices have been reduced. This results in a sudden increase in the engine speed. Particularly, when such a sudden increase in the engine speed occurs when a driver makes an engine stop request, the engine speed is increased despite the intention of the driver to stop the engine. This causes the driver to feel uncomfortable.